Mike,
Thanks for the speedy reply.  The query worked a treat (I am using version 7) and I am embarrassed to say that it showed up even more unsourced facts than I expected.
As an example it shows some sloppy thinking on my part in that I can see that I have been listing a lot of couples as "married" simply because they were living together (census data) or listed as parents; and not documenting the source of the reasoning.  I guess in these sort of situations I should technically  be listing the relationship as Unknown unless I have additional evidence.    Sadly it is not the only example of where I have been a bit lazy !
There is enough there to keep me busy for ages.
Thanks again for the pointer.
Albert Easton